Fiezo electric resonator



July 2, 1929.

EIEZO ELECTRIC RESONATOR Original Filed Jan. 28. 1920 A rrae NfY w. G. cADY Re. 17,359

' if compressed or otherwise strained in certain Reissued July 2, 192 9.

UNITED STATES Re. 11,359 PATENT: oFncE-Q WALTER G. (LADY, OF MIDDLETOWN, CONNECTICUT, ASSIGNOR TO RADIO CORPORA- TION OF AMERICA, A. CORPORATION OF DELAWARE.

. PIEZO-ELECTRIC RESONATOR.

Original No. 1,450,249, dated April 3, 1923, Serial No. 354,659, filed January 28, 1920. Application for reissue filed August 6, 192-5.

Serial No. 48,681.

DIvIsIoN E.

The present invention relates to electrical systems, and more particularly to systems comprising electro-mechanical vibrators.

' A chief object of the invention is to provide an improved method of, and system and apparatus for, transmitting'energy from one electric circuit to another. .Other objects will appear hereinafter, and will be particularly pointed out in the appended claims.

In the accompanying drawings, Fig. 1 is a'diagrammatic view of a circuit and ap paratus illustrating the principles underlying the present invention and Fig. 2 is a similar view, illustrating invention.

'For many years it has been known that quartz, tourmaline and certain other crystals,

directions, respond electrically, so as to enhibit positive and negative electrification in certain regions on their surfaces. It has also been known that the converse effect obtains,

that is to say, that such crystals, when elec trically stimulated, as by being placed in an electric field, become deformed. This phenomenon has been known as piezo-electricity.

In the specificationand the claims, the action of the electric forces to cause mechanical deformation will, for brevity, be called stimulation; and the development of the electromotive force by the deformation will be called response. A large number of both natural and artificial crystals have been found to posscss this piezo-electric property. The general knowledge on the subject has so far developed that it is now possible to predict in advance whether a given crystal will show the piezoelectric effect, and in what manner a plate or rod should be cut from the crystal inorder to exhibitthis'eifect to the greatest possible degree. '1

' The crystal that-has been most commonly employed in piezo-electric experiments, in the past, has been quartz. As a rule, investigators have used thin, flat plates or rods 1 of quartz rectangular in cross section, and coated 'on their opposite faces with tinfoil coatings 2,

' is is explained in my application Serial No. 20,277, filed April 2, 1925, for reissue of my Letters Patent No. 135.03%, of which the a preferred form of the present application is a division, such a plate or rod 1, Fig.1, the conducting coatings 2 of which are connected with a source of highceedingly minute, except when the frequency of the current approximates a natural frequency of mechanical vibration of the plate.

Even at this natural frequency, the changes in the dimensions of the plate resulting from its forced vibrations'are so minute as to escape detection under ordinary conditions. They are nevertheless sufficient to exert a marked reaction upon the electric current.

When the plate is made from a piezo-elec- 'tric crystal of good elastic qualities, such as quartz, when its width is small in comparison with its length, and it is mounted in such manner that its vibrations will be damped as little as possible, the reaction is extremely sharp and very pronounced. Such a plate, connected to a source of electric oscillations of variable frequency, will respond when one and only one frequencyneglecting for the moment overtone is being generated. It forms a piezo-electric resonator, somewhat analogous to the acoustical resonators of Helmholtz.

It is not necessary thatjghe device" comprise a long, narrow plate, althbiigh this has its advantages in permitting greater sharpness of tuning, and in securing greaterfreedom from effects that might be produced by undesired modes of vibration. For a coupling device between two circuits, it is advantageous to employ a relatively wide plate, since larger amounts of energycan then be transmitted;

The plate may have various shapes, or some I other form than a plate m'aybe used, includ 1 complicated the form'the more numerous are the frequencies to which the unit will respond. According to the invention illustrated in Fig. 2, this piczo-electric resonator is used to couple mechanically one high-frequency circuit to another in order to transmit energy from one to the other circuit at a certain particular frequency. In this figure, 1 is the piezo-electric resonator, having two pairs of coatings 7 and 8, one pair 7 of which is connected to the oscillating circuit 3, which contains also a coil 9 and a condenser 10, while the other pair of coatings 8 is connected to a similar oscillating circuit 11 containing a coil 12 and a condenser 13. The figure is in tended merelyito illustrate the general principles which apply to any of the numerous types of high-frequency circuit.

In this case, the following action takes place: Assuming that 3 represents the primary circuit, then, whenever an alternating current, at the critical frequency, flows in that circuit, the plate 1 will be brought into energetic vibration through the agency of the alternating potential differences between the "coatings 7. These vibrations, will, in turn,

generate potential differences in the coatings 8, which will cause an alternating current of the same frequency to flow in the secondary circuit 11. At other frequencies, the forced vibrations in the resonator 1 will be of very small amplitude, hence the induced current will be correspondingly small. The current flowing in the coil 12, at the frequency of the crystal, may be detected in any desired way, or it may be otherwise utilized.

vWhile the fundamental frequency of the plate or rod will usually give the strongest reaction, the various overtone vibrations can also be employed, giving reactions at frenot restricted to the exact embodiments there-,

plate or rod of piezo-electric crystal, a plural:

ity of pairs of conductive coatings applied to the regions of opposite electrification thereon,

and means for connecting such pairs of coatings to a corresponding number of alternating-current circuits, as herein described.

2. An alternating-current system comprising two resonant circuits, a piezo-electric body connected with one of the circuits, and means for transmitting energy from the said one circuit to the other circuit through the resonant vibrations of the body.

3. An alternating-current system comprising two resonant circuits, and means comprising a piezo-electric body connected with one of the circuits and so designed as'to react electrically upon the other circuit.

4. An alternating-current system comprising two resonant circuits, and means comprising a piezo-electric body designed to transfer energy from one of the circuits to the other circuit.

- 5. An alternating-current system compris-.

ing two circuits, and an electro-mecha'nical vibrator for coupling the circuits together and having two pairs of coatings, the vibrator being adapted to vibrate mechanically when stimulated electrically and to respond electrically when vibrated mechanically, one of the pairs of coatings being connected with one of the circuits and the other pair of coatings being connected with the other circuit.

6. A piezc-electric body having a plurality of pairs of conducting coatings, the elements of each pair being adjacent to regions thereof that exhibit opposite electrification when the body vibrates.

In testimony whereof, I hereunto aflix my signature. I

WALTER G. CADY. 

